Airfield lighting systems comprise a series of light fixtures used to provide various visual signals for airfield operations. These light fixtures are typically located in the airfield, which is an outdoor environment open to the elements. Thus, during cold weather conditions, snow and ice may accumulate on the emitting portions of the light fixtures, obstructing visibility of the light. In order to resolve this issue, heating elements are provided in the light fixtures which warm the light fixtures and melt away the snow or ice that may have accumulated. Typically, the heating elements are controlled by thermistors or other temperature sensing devices. The heating elements are typically turned on when the ambient temperature falls below a certain threshold, such as 38° F., and turned off when the temperature rises a few degrees higher. This results in the heating element being on for much longer than is needed to clear the snow or ice. Thus, a large amount of electricity is wasted.
Airfield lighting systems were traditionally designed using incandescent light fixtures as the load. In order to achieve consistent brightness across all the light fixtures in a circuit, a constant current regulator (CCR) was used to maintain a constant current across the circuit. Typically, a constant current regulator can provide a range of current levels, such as from 2.8 A to 6.6 A. More recently, airfield light fixtures are being retrofitted with light emitting diode (LED) light sources. However, these new LED light fixtures as well as the heating elements are still being powered through the legacy CCR systems. Thus, it is advantageous to provide control schemes that can be implemented using the legacy CCR.